The controller uses one or more ordinary silicon diodes as a sensor, and uses a cheap opamp as the amplifier. I designed this circuit to use 12V computer fans, as these are now very easy to get cheaply. These fans typically draw about 200mA when running, so a small power transistor will be fine as the switch. I used a BD140 (1A, 6.5W), but almost anything you have to hand will work just as well.
Read more original source: http://sound.westhost.com/project42.htm
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This entry was posted on Saturday, October 25th, 2008 at 4:15 am and is filed under 741, detector, Electronic Control.
